The present invention relates to release mechanisms for toggle-locking hand pliers. In particular, it relates to a structure for retaining compound toggle linkages for locking and releasing hand tools used for clinching onto various workpieces and remaining locked thereto without being held continuously by the worker.
Toggle-locking pliers typically utilize a movable jaw and a fixed jaw to firmly grasp and lock onto a workpiece. Typically, the movable jaw may be adjusted to grasp the workpiece as the handles are compressed together. As the handles are more tightly compressed, the toggle mechanism will lock the hand tool onto the workpiece. After the user releases the handles, the tool will remain firmly locked in place. Adjustments to the clamping force may generally be made by rotating an adjusting screw in the base of the fixed handle. By rotating the screw, the configuration of the toggle mechanism of the pliers is modified, thereby providing more or less relative force between the handle position and the position of the closed or open jaws.
Conventional toggle locking pliers include three pivot points in what is known as the xe2x80x9cpower linexe2x80x9d from the pivot point of the movable handle on the movable jaw down through an inner pivot near the end of the spanning toggle link. The other end of the toggle link rests pivotably at the tip of the adjusting screw in the channel of the fixed handle. Locking the handle causes the center pivot point to cross the xe2x80x9cpower linexe2x80x9d between the two outer pivots. Unlocking the conventional locking hand tool involves forcing the single center pivot back across the xe2x80x9cpower linexe2x80x9d. Usually, this is carried out by means of a release lever pivotably mounted in the channel of the movable handle. The release lever is pushed against a projection on the toggle link, thus causing the toggle link to pivot outward and drive the two handles apart to release the clamping action of the jaws.
An alternative to the release lever arrangement is shown in U.S. Pat. No. 5,056,385. This patent discloses a five-pivot toggle mechanism located between the fixed and movable handles of a toggle-locking hand tool, with a compound toggle linkage mechanism fitting inside the channel of the movable handle. The spanning toggle link is of a conventional design with a transverse projection located near the midpoint. The projection, upon clamping the handles together, fits into the channel of the movable handle acting as a stop to limit closure. An added or second link is pivotably mounted completely within the channel of the movable handle. In the closed locking position, the second or compound link extends from a contact with the projection of the spanning link past the end of the spanning link. The spanning link is pivoted to the compound link. The spanning link further extends to an additional pivot on the movable handle between the pivot point for the spanning link and the conventional pivot point for the movable handle with the movable jaw.
This compound linkage greatly increases the mechanical advantage of the movable handle. Thus, a small urge by the user outward at the inside end of the movable handle springs the two inner pivot points of what is now a four point xe2x80x9cpower linexe2x80x9d of the locking hand tool back across the xe2x80x9cpower linexe2x80x9d, thus unlocking the tool with minimal wear.
The compound linkage arrangement shown in U.S. Pat. No. 5,056,385 tends to allow the compound link to extend beyond the width of the movable handle in some unlocked configurations. Furthermore, the configuration of the compound link may have some shortcomings with respect to user feedback and the ability of the user to sense when toggling has taken place.